Antibodies to estradiol-17B, estrone and progesterone will be used to study the hormonal requirements for normal ovum transport through the rabbit oviduct. Antisera against these hormoneswill be produced in ovariectomized sheep, characterized as to specificity and titer, and injected into rabbits singly or in combination to cause passive immunity. The results of passive immunity on ovum transport and the blood plasma levels of the three steroids will be determined.